1. Technical Field
The present invention relates to a line head and an image forming apparatus provided with the line head.
2. Related Art
An image forming apparatus has been conventionally used in the forming of an image on a recording medium. In such an image forming apparatus, a photo conductor of a circular column shape (cylindrical shape), an electrification unit which uniformly electrifies a light receiving surface of the photo conductor, an exposure unit (line head) which forms an electrostatic latent image on the light receiving surface by emitting light such as a laser onto a desired position of the uniformly electrified light receiving surface, and the like are provided.
Further, as the exposure unit (line head) which is provided in the image forming apparatus, there is known an optical information writing device having a plurality of LED chip arrays arranged in a line in the axial direction of the photo conductor, and an optical lens system which is provided with a plurality of lens elements each provided corresponding to each LED chip array (for example, JP-A-2-4546).
In the optical information writing device described in JP-A-2-4546, the optical lens system is disposed such that the light from each LED chip array is imaged on the light receiving surface of the photo conductor (that is, a spot diameter on the light receiving surface is minimized), and, for example, by independently controlling the ON/OFF timing of the driving (light emission) of each LED, it is possible to form a desired latent image on the light receiving surface.
Here, it is difficult to make the transverse cross-sectional shape of the photo conductor into an exact circle in terms of technology and cost, and even if it is possible to make the transverse cross-sectional shape of the photo conductor into an exact circle, its shape varies according to the usage environment (atmosphere temperature or external force), the deterioration of the light receiving surface, or the like, whereby there is also a case where the transverse cross-sectional shape does not become an exact circle. In this manner, in a case where the transverse cross-sectional shape of the photo conductor is not an exact circle, at a first point on the light receiving surface, the light receiving surface is coincident with an imaging point, but, at a second point different from the first point, the light receiving surface is not coincident with the imaging point. In this manner, a difference occurs in the size of the spot at the first point and the second point, so that it is not possible to form spots of a uniform size with respect to the entire area of the light receiving surface.
Further, as described above, although the exposure unit is provided so as to minimize the spot diameter on the light receiving surface, in a case where the installation position of the exposure unit has deviated from a predetermined position (that is, in a case where the separation distance between the exposure unit and the photo conductor has deviated from a predetermined value), the spot diameter on the light receiving surface becomes larger than the predetermined diameter.
As described above, in the optical information writing device described in JP-A-2-4546, it is difficult to form a spot having a desired diameter on the light receiving surface, so that there is a problem that it is difficult to form a desired latent image.